Earth-boring tools are commonly used for forming (e.g., drilling and reaming) bore holes or wells (hereinafter “wellbores”) in earth formations. Earth-boring tools include, for example, rotary drill bits, core bits, eccentric bits, bi-center bits, reamers, underreamers, and mills.
Different types of earth-boring rotary drill bits are known in the art including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), roller cone bits (which are often referred to in the art as “rock” bits), diamond-impregnated bits, and hybrid bits (which may include, for example, both fixed cutters and roller cones). The drill bit is rotated and advanced into the subterranean formation. As the drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore.
The drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a “drill string,” which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of the formation. Often various tools and components, including the drill bit, may be coupled together at the distal end of the drill string at the bottom of the wellbore being drilled. This assembly of tools and components is referred to in the art as a “bottom hole assembly” (BHA).
The drill bit may be rotated within the wellbore by rotating the drill string from the surface of the formation, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is also coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is mounted, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore.
The cutting elements used in earth-boring tools often include polycrystalline diamond cutters (often referred to as “PDCs”), which are cutting elements that include a polycrystalline diamond (PCD) material. Such polycrystalline diamond-cutting elements may be formed by sintering and bonding together relatively small diamond grains or crystals under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may be drawn into the diamond grains or crystals during sintering and serve as a catalyst material for forming a diamond table from the diamond grains or crystals. In other methods, powdered catalyst material may be mixed with the diamond grains or crystals prior to sintering the grains or crystals together in an HTHP process.
Cutting elements may become worn during use in a drilling operation. Worn cutting elements may be less effective at cutting the subterranean formation. In addition, as cutting elements wear, they become more and more likely to fail. Failure of cutting elements can result in pieces of hard material becoming dislodged from earth-boring tools, the pieces becoming obstacles to further drilling. For example, broken cutting elements may abrade the earth-boring tool as the broken cutting elements pass up the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore. Since the cutting elements may be much harder than the subterranean formation, earth-boring tools may not be able to cut through broken pieces of cutting elements. In some cases, the presence of broken cutting elements within a wellbore may force the operator to redrill the wellbore with a different tool or drill around the damaged cutting elements. To prevent breakage of cutting elements and costs associated with such breakage, an operator may remove an earth-boring tool from service well before its useful life is over. Such premature removal costs operators in both time and money if the earth-boring tool could have safely remained in service. It would therefore be beneficial to have a method to determine the amount of useful life remaining in an earth-boring tool without removing the tool from a wellbore.